Three-phase high voltage cable arrangement having cross-bonded cable screens and cross-bonded water sensing wires

ABSTRACT

A cable arrangement where three cables have at least two cross-bonding locations when transmitting power between a first location and a second location. At the cross-bonding location not only the screens but also the water sensing wires are cross-bonded in cross-bonding devices. Thus, voltage differences between the water sensing wires and the screens of the respective cables in the three-phase system can be avoided. A particular application is found in high power transmission systems using high voltage cables.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase application based onPCT/EP01/03625, filed Mar. 29, 2001, the content of which isincorporated herein by reference, and claims the priority of EuropeanPatent Application No. 1007008.5, filed Mar. 31, 2000, the content ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a three-phase high voltage cable arrangementfor transmitting power from a first location to a second location over apredetermined distance of e.g. a few km. In particular, the inventionrelates to such a three-phase high voltage cable arrangement where thescreens of the cables are cross-bonded at a particular screencross-bonding location at least twice over said distance.

The cables of the cable arrangement in accordance with the inventionalso comprise at least one water sensing wire for sensing waterintrusion into the respective cable. For such a three-phase high voltagecable arrangement the invention in particular addresses the problem howdifference voltages between the water sensors and the cable screens canbe avoided without using a high voltage protection device.

BACKGROUND OF THE INVENTION

FIG. 1 shows a typical three-phase high voltage cable arrangement CA fortransmitting power from a first location A to a second location Bincluding a first, second and third high voltage cable L1, L2, L3 fortransmitting the respective currents of each phase R, S, T. A typicaldistance is 1-2 km.

The individual cables L1, L2, L3 have a typical construction of a highvoltage cable as shown in FIG. 2. A conductor 1 is surrounded by aninsulation 3 and the insulation is surrounded by a screen 5 and an outercoating 6. The screen can have a cross section of 35-50 mm² and has avery high conductivity of ≈0,017 Ωmm². Preferably, the screen is made ofcopper.

Furthermore, the conductor 1 may be surrounded by an inner conductinglayer 2 and the insulation 3 may be surrounded by an outer conductinglayer 4. These layers have low conductivity and are sometimes alsocalled “semiconducting” layers. Such a cable construction is typicallyused for high voltages of >10 kV.

In a cable arrangement including three different cables L1, L2, L3 eachhaving a construction as shown in FIG. 2 losses occur. The total lossescan be divided into two types, namely losses that only occur if currentis flowing in the cable system (current-related losses) and losses whichare produced solely by the effect of the electrical field in theinsulation (voltage-dependent losses). The current-dependent losses donot only occur in the current-carrying conductor itself (conductorlosses) but also as so-called additional losses in the other metallicelements of the cable system where eddy and circulating currents areinduced under the effect of the magnetic field of the current-carryingconductor. The conductor losses are for example Joule losses and alsodue to skin and proximity effects.

The most important additional losses are those caused by the axialinduction currents in the metallic screen. Such additional losses in thecable sheath, screen and other metallic system components can be reducedby use of non-magnetic steel for armouring to prevent magnetic reversallosses, by grounding of the screens or metal sheaths at one end to avoidproviding a closed loop for the induction currents, or by a so-called“cross-bonding” of the cable sheaths or screens to largely compensatethe induction voltages such that the screen/sheath current andconsequent losses are minimized in spite of the entire arrangement beinggrounded at both ends.

In the cross-bonding technique the cable arrangement is subdivided intothree cable sections FCS, SCS, TCS and at two cross-bonding locationsSCB1, SCB2 the screens 5 are cyclically connected such that the totallyinduced sheaths or screen voltage adds up to zero over the entirelengths, as shown in the bottom graph in FIG. 1.

Such techniques are described by Egon F. Peschke and Rainer vonOhlshausen in “Cable Systems for High and Extra-High Voltage”,Publicis-MCD-Verlag 1999, ISBN 3-89578-118-5, pages 58-62.

PRIOR ART OF THE INVENTION

The screen 5 surrounding the insulation 3 of the cable shown in FIG. 2typically consists of a wire braiding, possibly covered with analuminium layer and extruded with another coating. The aluminium layercan additionally prevent the intrusion of water into the respectivelayers of the cable. Also the use of a lead coating and aluminium sheathis known.

High voltage cables having an insulation 3 of cross-polyethylene areparticularly prone to humidity problems. Such cables must have apermanently waterproof outer coating, since the presence of water in thescreen region can cause aging of the insulation by “water treeing”. Inprinciple, water can only intrude into the screen or other parts of thecable if the outer coating 6 is destroyed or damaged during the lifetimeof the cable. Such damages can however not be excluded over an operationlifetime of 30-50 years, e.g. if the cable is damaged accidentally whendigging the ground.

To detect the intrusion of water into the screen immediately and tolimit the damage to the system by an immediate repair high voltagecables can be equipped with electric water sensors. These water sensorsare typically in the form of water sensing wires 7 as indicated in FIG.2 and FIG. 3. These water sensing wires 6 can be arranged anywhere inthe layered structure of the cable. Preferably, in composite-layercoating cables the water sensing wires 7 are arranged between the wiresof the screen 5 as in particular shown in FIG. 3. The wires 7 can bearranged in symmetry to the core 1 (diametrically) or may be spirallywound around the core 1.

As described by L. Goehlich, W. Rungseevijitprapa and H. Vemmer in“Wassermonitoring-System für VPE-Hochspannungskabel” inElektrizitätswirtschaft, Jahrgang 97 (1998), Heft 1-2, typically a watermonitoring system for the detection and locating of insulation errors asshown in FIG. 4 can be provided. A simple electric method is used inwhich a DC voltage is applied between the water sensor 7 and the cablescreen 5 and a current flow is generated between the cable screen 5 andthe water sensor 7 if there is a water intrusion. Furthermore, thesystem can measure DC currents between a water sensing wire 7 and thescreen 5 of an adjacent cable in order to provide various measurementvalues for the water intrusion. Whilst a single water sensing wire 7 issufficient, FIG. 3 shows a configuration where two water sensing wires 7are used for redundancy purposes.

FIG. 5 shows a typical connection of the cables at a cross-bondinglocation where the cross-bonding is performed by connectingcross-bonding connection wires SCBCR, SCBCS, SCBCR with the screens 5 ofthe left-hand side cables L1, L2, L3 and the screens 5′ of theright-hand side cables L1′, L2′, L3′ in respective connectors (joints)CC1, CC2, CC3. These cross-bonding connection wires are then led to across-bonding device SCBD where the actual cross-bonding is carried out.Whilst in FIG. 5 the cross-bonding is carried out with respect to ajoint where three first section cables L1, L2, L3 and three secondsection cables L1′, L2′, L3′ are connected at their conductors 1, thecross-bonding location need not necessarily be at these conductor jointconnectors. Alternatively, the cables can be connected arbitrarily atjoints in accordance with the cable length requirements and thecross-bonding can be carried out by opening only the cable insulationand performing the cross-bonding independently of the mechanicalconnection of the conductors at the joints.

As shown in FIG. 5 and FIG. 3, at the connectors and in fact throughoutthe entire extension of the cable arrangement the water sensing wires 7(two are shown as an example in FIG. 5) run parallelly to the conductor1 and simply run through the respective joints. The cross-bonding of thescreens is carried out such that the screen of cable L1 in section FCSis connected with the screen of the cable L1′ in section SCS and thescreen of cable L1′ in section SCS is connected with the screen of cableL1″ in section TCS e.g. at respective joints or elsewhere along theextension of the cable allows, to add up the induced voltages thuspreventing currents and losses in the screen. However, also in the watersensing wires 7 voltages are induced by the currents in the conductor.To not destroy the insulation of the water sensing wires (as shown inFIG. 3 the water sensing wire is a Cu-wire with a polymer insulation)and the outer water sensing circuitry (see FIG. 4) the inventors haverecognized that the difference voltages between the cable screen and thewater sensing wire should not exceed some 10 V. The causes of suchdifference voltages between the cable screen and the water sensor are:

-   induction voltage as a result of the rated current in the conductors    of the cables;-   induction voltage as a result of a short circuit current in the    conductor; and-   travelling waves caused by lightning when there is a connection to    overhead wires.

Whilst such induced voltages and the electrical losses as a result ofthe electrical properties of the screen are small when using short cableconnections and cables with small conductor cross sections (thedifference voltage between the screen and the water sensing wire issmall) the inventors have recognized that significant differencevoltages between the screen and the water sensor occur at great lengthof the cables, even if the losses in the screen with grounding thescreens at both ends (see FIG. 1) are prevented by the cross-bonding ofthe screens. In particular at the joints (connectors) large voltagesoccur with respect to the water sensing wires. Furthermore, of courseinduced voltages on the water sensing wires cause incorrect measurementresults in the water monitoring system and may even lead to a damage ofcomponents therein.

To prevent a countermeasure against induced voltages on the water sensorwires, conventionally additional components like excess voltageprotectors in the form of semiconductor switching elements (e.g. TRIACSor thyristers) are used. However, such excess voltage protectors canonly prevent excess voltages of short duration with limited power.

SUMMARY OF THE INVENTION

As described above, even if the connectors (joints) are well designed tominimize as much as possible the generation of induced voltages on thewater sensing wires and even when using excess voltage protectors, therestill exists the problem of the generation of high difference voltagesbetween the water sensors and other parts of the cable, e.g. the screen,which cannot be satisfactorily be avoided with conventional excessvoltage protectors, in particular at great length of the cablearrangement.

Therefore, the object of the invention is to provide

-   a three-phase high voltage cable arrangement in which high    difference voltages between the water sensing wires and other parts    of the cable are avoided without using additional components like    excess voltage protectors.

SOLUTION OF THE OBJECT

This object of the invention is solved by a three-phase high voltagecable arrangement for transmitting power from a first location to asecond location including a first, second and third high voltage cable,each high voltage cable having a conductor and a screen wherein thescreens are cross-bonded twice over said distance at particularcross-bonding locations to cancel out the screen voltages, wherein saidfirst, second and third cable each comprise at least one water sensingwire for sensing water intrusion into the respective cable and saidwater sensing wires are cross-bonded twice over said distance at saidcross-bonding locations wherein the cross-bonding of the water sensingwires is performed in the same cyclic order as the cross-bonding of thescreens to cancel out difference voltages between the water sensor wiresand the cable screens.

According to the invention, in a cable arrangement with cables includingwater sensors e.g. in the cable screen and with cyclically cross-bondedcable screens, it is suggested to cross-bond the water sensor wires inthe same cyclic order as the cable screens. If the water sensors arecross-bonded in the same manner as the screens difference voltages canbe completely avoided between the water sensing wires and the screen.

The cross-bonding locations can be arranged at the joints or anywherealong the extension of the cable arrangement where the cable coating isopened for cross-bonding. Preferably, at each cross-bonding location afirst, second and third pair of water sensing wire cross-bondingconnection cables are connected with the respective water sensing wiresand a first, second and third screen cross-bonding connection cable isconnected with the respective screens of the respective cables. Thewater sensing wire cross-bonding connection cables and the screencross-bonding connection cables are preferably connected with a watersensing wire cross-bonding device and a screen cross-bonding device.

The water sensing wire cross-bonding device and the screen cross-bondingdevice can be arranged into different cross-bonding boxes or in a singlecommon cross-bonding box.

Further advantage embodiments and improvements of the invention can betaken from the dependent claims. Furthermore, it should be noted thatthe invention can comprise embodiments which result from a combinationof features separately described in the specification and/or claimed inthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cable arrangement where a cross-bonding of screens isperformed at two screen cross-bonding locations according to the priorart;

FIG. 2 shows a principle cable construction of the cables shown in FIG.2, in particular incorporating water sensing wires embedded in thescreen;

FIG. 3 shows a cable construction as in FIG. 2, in particular theprovision of two water sensing wires arranged between the wires of ascreen;

FIG. 4 shows a block diagram of a water monitoring system according tothe prior art;

FIG. 5 shows the connection of screen cross-bonding connection wires atrespective joints of the screen-cross-bonding locations shown in FIG. 1;

FIG. 6 shows a circuit diagram for performing a cross-bonding of cablescreens as well as water sensing wires at a cross-bonding location;

FIG. 7 shows a similar diagram as in FIG. 5, however comprisingadditional water sensing wire cross-bonding connection cables;

FIG. 8 shows a screen cross-bonding device for cross-bonding of thescreens;

FIG. 9 a shows a top view of a water sensing wire cross-bonding devicefor cross-bonding of the water sensing wires;

FIG. 9 b shows a side view of the water sensing wire cross-bondingdevice shown in FIG. 9 a;

FIG. 10 shows a cross-bonding box used for performing a cross-bonding ofthe water sensing wires as well as the screens of the cables; and

FIG. 11 shows a cross-bonding location with a device for leading out thescreen cross-bonding and water sensing wire cross-bonding connectioncables.

In the drawings the same or similar reference numerals denote the sameor similar parts throughout.

PRINCIPLE OF THE INVENTION

Hereinafter, the principle of the invention will be described withreference to FIG. 6.

In FIG. 6 a cross-bonding location CBL of the inventive cablearrangement CA is shown. Such a cross-bonding location corresponds tothe screen cross-bonding locations SCB1, SCB2 shown in FIG. 1. The cablearrangement CA comprises first, second and third high voltage cables L1,L2, L3 and each high voltage cable has a conductor (not shown), a screen5 and at least one water sensing wire 7. As explained above withreference to FIG. 3, of course, several water sensing wires 7 can beprovided in each cable, however, for a better overview of thecross-bonding only one single water sensing wire 7 is respectivelyillustrated.

Furthermore, of course, it will be appreciated that the correspondinglocation CBL where the water sensing wires and the screens are bothcross-bonded in the same cyclic order is provided twice along thedistance between the first location A and the first location B.Furthermore, as also explained above, the cross-bonding location CBL maybe arranged at the respective joint where the conductors are joined orcan be located anywhere along the length of the cables in which case theouter coating and respective other layers of the cable construction isopened to allow access to the water sensing wires and the screens.

At the cross-bonding location CBL the screens as well as the watersensing wire of the respective cable L1, L2, L3 are separated in orderto allow the cross-bonding. Thus, at the cross-bonding location CBL thefirst cable Li has on the left side a first left screen 5 _(1L) and afirst left water sensing wire 7 _(1L) and on the right side a firstright screen 5 _(1R) and a first right water sensing wire 7 _(1R).Similarly, the second cable L₂ has a second left and second right screen5 _(2L), 5 _(2R) and a respective second left and right water sensingwire 7 _(1L), 7 _(2R). The third cable L3 has respective screens 5_(3L), 5 _(3R) and water sensing wires 7 _(3L), 7 _(3R). A wirecross-bonding device WCBD is provided for performing the cross-bondingof the water sensing wires and a screen cross-bonding device SCBD isprovided for performing the conventional screen cross-bonding.

As shown in FIG. 6, in the wire cross-bonding device WCBD the left firstwire 7 _(1L) is connected with the second right wire 7 _(2R). The secondleft wire 7 _(2L) is connected with the third right wire 7 _(3R). Thethird left wire 7 _(3L) is connected with the first right wire 7 _(1R).Preferably, to add further protection, surge arrestors A_(1L), A_(2L),A_(3L), A_(1R), A_(2R), A_(3R) are provided between the respective wires7 _(1L), 7 _(2L), 7 _(3L) and the screens 5 _(1L), 5 _(2L), 5 _(3L) andthe wires 7 _(1L), 7 _(2L), 7 _(3R) and the screens 5 ₁R, 5 ₂R, 5 ₃R.Such arrestors can be surge arrestors for 200V.

In the screen cross-bonding device SCBD the first left screen 5 _(1L) isconnected with the second right screen 5 _(2R), the second left screen 5_(2L) is connected to the third left screen 5 _(3L) and the third rightscreen 5 _(3R) is connected to the first right screen 5 _(1R). ArrestorsA_(S1), A_(S2), A_(S3) can preferably be connected as additionalprotection devices between the first right screen 5 _(1R), 5 _(2R), 5_(3R) and ground. Such arrestors can be surge arrestors for 5000V.

As can be seen from FIG. 6, according to the principle of the invention,the water sensing wires 7 are cross-bonded in the same cyclic order asthe cross-bonding of the screens. By this measure no difference voltageoccurs between the individual parts of the cables L1, L2, L3, e.g.between the sensing wires 7 and the screens 5.

First Embodiment

FIG. 7 shows a first embodiment of the invention where the cross-bondingin accordance with FIG. 6 takes place at a joint where the three cablesL1, L2, L3 are joined at their conductors 1. R, S, T in FIG. 7respectively correspond to the R, S, T phase of the three-phase cablearrangement CA.

The designations of the screens 5 and the wires 7 correspond to thoseshown in FIG. 6. In FIG. 7 the joint is made of three connection partsCC1, CC2, CC3 which can be part of the joint for joining the conductors1. However, it should be understood that the cross-bonding location CBLshown in FIG. 7 may also be located elsewhere along the line, i.e. notat a joint but at a location where the outer coating of the respectivecables L1, L2, L3 is opened to allow the connection of the connectioncables SCBCR, SCBCS, SCBCT.

In FIG. 7 the first screen connection cable SCBCR has its conductinglayer connected to the first left screen 5 _(1L) and its core conductorconnected to the first right screen 5 _(1R). The second screenconnection cable SCBCS has in a similar fashion connected its conductinglayer to the second left screen 5 _(2L) and has its core conductorconnected to the second right screen 5 _(2R). Furthermore, the thirdscreen connection cable SCBCT has its conducting layer connected to thethird left screen 5 _(3R) and its core conductor connected to the thirdright screen 5 _(3R).

In addition, there are provided three pairs of wire connection cablesRL, RR; SL, SR; TL, TR. A first wire connection cable RL of the firstpair has its core conductor connected to the first left wire 7 _(1L) andhas its conducting layer RL_(s) connected to the first left screen 5_(1L). The second wire connection cable RR of the first pair has itscore conductor RR_(c) connected to the first right wire 7 _(1R) and hasits conducting layer RR_(s) connected to the first right screen 5 _(1R).In the same manner the first and second wire connection cable SL, SR areconnected to the second left screens and wires and to the second rightscreens and wires. Likewise, the two wire connection cables TL, TR arerespectively connected to the third left screens and wires and to thethird rights screens and wires of the third cable L3. The first, secondand third pair of water sensing wire connection cables and the first,second and third screen connection cables SCBCR, SCBCS, SCBCT areconnected with a cross-bonding device. As will be explained with furtherdetails below, the cross-bonding device can be provided in two separatecross-bonding boxes for respectively cross-bonding of the water sensingwires and of the screens. Alternatively, a single cross-bonding box canbe used to perform simultaneously the water sensor wire cross-bondingand the screen cross-bonding which improves the impedance matching. Thiswill be explained below with reference to the embodiments in FIGS. 8-10.

The connection cables RL, RR; SL, SR; TL, TR; SCBCR, SCBCS, SCBCT can becoaxial cables. Preferably, the coaxial cables should have a conductorcore which has the same wave impedance as the water sensing wires andthe screens, respectively. By this measure, travelling waves on thecable screen are not reflected with respect to the water sensing wireand there will not be generated an excess voltage between the strands ofthe cable.

Second Embodiment

FIG. 8 shows an embodiment of the screen cross-bonding device SCBD forperforming the cross-bonding of the screens of the three cables L1, L2,L3. AS shown in FIG. 8, the screen cross-bonding device SCBD has theform of a box including a housing SCBDH and insertion parts RI, SI, TIinto which the respective screen cross-bonding connection cables SCBCR,SCBCS, SCBCT are inserted, e.g. clamped or otherwise fixed. On theinside of the housing CBDH the conductor cores CR, CS, CT and thescreens or conducting layers SR, SS, ST are exposed. Furthermore,connection rails RAR, RAS, RAT are provided to connect the conductorcores CR, CS, CT and the screen SR, SS, ST as principally indicated inthe circuit diagram in FIG. 6.

That is, a first rail RAR connects the conductor core CR with the screenST of the third cable SCBCR. The second rail RAS connects the secondcore conductor CS of the second cable SCBCS with the screen SR of thefirst cable SCBCR. Furthermore, the third connection rail RAT connectsthe third core conductor CT of the third cable SCBCR with the screen SSof the second connection cable SCBCS.

The first, second and third rails RAR, RAS, RAT can have the form ofelongated plates and are preferably made of Cu. The plates are furtherconnected with high voltage protectors OVPR, OVPS, OVPT which areconnected to ground at the other terminals (not shown in FIG. 8). Theseovervoltage protectors correspond to the search arrestors A_(S1),A_(S2), A_(S3) shown in FIG. 6. The overvoltage protectors OVPR, OVPS,OVPT are provided in order to limit transient difference voltagesbetween the screens and water sensing wires to a value below thebreakdown voltage of the insulation of the water sensing wire. As shownin FIG. 3, the water sensing wire is surrounded by a particularinsulation layer.

The individual connection plates for connection rails RAR, RAS, RAT inthe connection box SCBD have a withstand voltage with respect to eachother and with respect to the environment which is larger than the breakdown voltage of the sheath voltage limiters as well as the test voltageto measure the tightness of the sheath which is in the range of some1000V. A typical voltage for the DC voltage test regarding the tightnessof the sheath is 5 kV. In this connection it should also be noted thatthe connection cables RL, RR; SL, SR; TL, TR; SCBCR, SCBCS, SCBCT neededfor the connection between the cables and the cross-bonding box have awithstand voltage which is same as the connection rails RAR, RAS, RAT.

Third Embodiment

FIG. 9 a shows an embodiment of the wire cross-bonding device WCBD asschematically indicated in FIG. 6. FIG. 9 a is the top view and FIG. 9 bis a cross-sectional view seen from the left in FIG. 9 a.

The wire cross-bonding device WCBD has the form of a box and receivesthe water sensor wire cross-bonding connection cables RL, RR; SL, SR;TL, TR. These cables are fixed at the housing 9 by means of a screw 11and a nut 12. Each cross-bonding connection cable is fed inside thehousing 9 to a respective plate connector PCR_(e), PCS_(e), PCT_(e);PCR_(r), PCS_(r), PCT_(r) each including a conductor board 14, e.g. aprinted circuit board PCB. The printed circuit board 14 is elevated fromthe ground by means of the screws 20 and distance elements 19 shown inFIG. 9 b.

The printed circuit board 14 carries two clamps 18, the excess voltageprotectors 15 (more precisely the excess voltage protectors A_(1L),A_(2L), A_(3L); A_(1R), A_(2R), A_(3R) as shown in FIG. 9 a), ashort-circuit plug including a socket 17 and short and longcross-bonding wires CBR_(L). CBS_(L), CBT_(L); CBR_(S), CBS_(S), CBT_(S)are respectively connected with the left and right clamps 18. Thecross-bonding wires correspond to the interconnections shown in FIG. 6.The bottom mounting board 13 is mounted to the housing bottom wall bymeans of screws 21. As shown in FIG. 9 b, the housing 9 has a removablecover which carries a specification plate 22.

As shown in FIG. 9 a, the short and long cross-bonding wires arerespectively connected with the left and right clamps 18 mounted on thePCB 14. These cross-bonding wires are permanently fixed in thecross-bonding device WCBD and during the mounting of the cross-bondingconnection cables RL, RR; SL, SR; TL, TR, the respective ends of theconductor cores RL_(C), RR_(C); SL_(C), SR_(C); TL_(C), TR_(C) (see FIG.7) and the respective screens RL_(S), RR_(S); SL_(S), SR_(S); TL_(S),TR_(S), are soldered at the solder points for the water sensor and thesolder points for the screen on the respective circuit boards 14. Sincethe circuit board 14 is elevated from the bottom wall of the housing 9as shown in FIG. 9 b, the respective core conductors and screens are fedto the board 14 from below and are then soldered on the top surface ofthe printed circuit board. As indicated with the reference numeral 14′the printed circuit board 14 carries a conductor pattern 14′ whichallows to make contact between the respective core conductors andscreens and the respective clamps 18 and thus with the short and longcross-bonding wires.

Of course, during the mounting of the cross-bonding connection cablesthe order of the cables must be observed in order to achieve theelectrical connection as shown in FIG. 6. However, otherwise only thesoldering of the respective core conductors and screens must beperformed to the circuit board 14 which thus enables a very quick andeasy connection of the water sensing wire cross-bonding device WCBD tothe cross-bonding connection cables.

As shown in FIG. 9 a, the connection board (printed circuit board) 14 isequipped with a plug terminal which allows the connection of the screenand the respective conductor cores. However, it also allows theconnection of measurement equipment such that the electricalcharacteristics of the respective water sensing wires can be determinedbefore a special selection of one or more of the water sensors.

The embodiment shown in FIG. 9 a of the water sensing wire cross-bondingdevice WCBD into which the cross-bonding connection cables shown in FIG.7 are inserted is usable for a water sensing system where only a singlewater sensing wire per cable L1, L2, L3 is employed. In this case therespective cross-bonding connection cables can be coaxial cables suchthat in the cross-bonding box WCBD only six coaxial cables are supplied.In this case, the water sensing wires in the joints CC1, CC2, CC3 arealso connected with coaxial cables. The outer conducting layer of thecoaxial cables are connected with the cable screen and the conductorcore of the coaxial cable is connected with the water sensing wire.Thus, per joint CC1, CC2, CC3 there is one coaxial cable for the screensand two coaxial cables for the respective left and right water sensingwires as shown in FIG. 7. A special embodiment of such a joint will bediscussed below with reference to FIG. 11.

Comparing the screen-cross-bonding device SCBD in FIG. 8 with the watersensing wire cross-bonding device DCBD in FIG. 9 a it is quite clearthat the cross-bonding wires in FIG. 9 a only require a smallcross-section and a small insulation to carry short-circuit currentssince lower difference voltages of ≈200V may occur whilst thecross-bonding rails RAR, RAS, RAT in FIG. 8 need a large cross-sectionfor large short-circuit currents due to the higher voltages of ≈5000V.

Furthermore, it should be noted that the cross-bonding device WCBD inFIG. 9 a is especially provided for a high voltage cable system withthree cables L1, L2 and L3 which have a screen and two water sensingwires 7 are diametrically arranged. In this case, the cross-bondingconnection cables are cables having a screen and insulation and twoconductor cores to which the respective water sensing wires and thescreen of the respective cable is connected. The cross-bonding deviceWCBD can then be used for the two water sensors, i.e. the two conductorcores of the cross-bonding connection cables are soldered at therespective two solder points on the printed circuit board 14 as shown inFIG. 9 a and can then be selected as described above. In the respectiveplate connectors PCR_(L), PCS_(L), PCT_(L); PCR_(R), PCS_(R), PCT_(R)the respective cross-bonding wires have the following assignment of thewires for the cross-bonding as shown in table 1 below:

TABLE 1 Joint left Joint right Coaxial cable Joint Coaxial cableConductor Conductor screen core Joint screen core L1 Inside L1 I L2Outside L2 A L2 Inside L2 I L3 Outside L3 A L3 Inside L3 I L1 Outside L1A

In table 1 the designations of L1 I, L2 I, L3 I denote the innerconnection and L1 A, L2 A, L3 A denote the outer connection. Inner andouter connection are related to the inner and outer conductor of thecoaxial cross bonding cable of the cable screen. The wire designationsL1 I, L2 I, L3 I; L1 A, L2 A, L3A respective denote the first and secondcore conductor of the cross-bonding connection tables RL, RR; SL, SR;TL, TR as principally indicated in FIG. 7. Thus, the cross-bondingconnection cables are connected with the respective printed circuitboard 14 at the respective solder points such that the sensor connectioncables are connected at the screen and at the wire with a respectiveovervoltage protector A_(1L), A_(2L), A_(3L); A_(1R), A_(2R), A_(3R)through the plug and socket arrangement 16, 17. After selection of thesensor, the non-used sensor is bridged with a prepared connection line.Because one sensor is for redundancy, the used (active) sensor has to bechosen by means of an electric measurement. The non-used (non-active)sensor has to be connected with the respective cable screen to avoidpotential differences. Then, the cross-bonding wires will allow across-bonding of the water sensing wires, i.e. the selectedcross-bonding wires. Thus, the cross-bonding device WCBD can be used forthe selection of one of two water sensing wires and one can select itwithout any danger of confusion. Since solder connections are used withrespect the plate connectors PCR, the cross-bonding connection cablescan also be easily removed and for the aim of any HV DC test new cablescan be mounted without any risk of confusion.

Finally, it should be noted that in FIG. 9 a only six plated connectorsare shown for allowing a selection of one of the two water sensors.However, it is of course possible that the plate connectors areconfigured to only have a single solder point on the printed circuitboard 14 such that cables with only one water sensing wire can becross-bonded. On the other hand, of course it is possible to configurethe plate connectors in such a manner that also more than two watersensing wires can be cross-bonded. Depending on the number of watersensing wires to be cross-bonded, the number of plate connectors and thenumber of cross-bonding wires can also be correspondingly increased.

Fourth Embodiment

FIG. 10 shows a further embodiment of the cross-bonding device similarto FIG. 8, However, the cross-bonding device CBD in FIG. 10 is not onlyused for the cross-bonding of the screens as was explained withreference to FIG. 8, but also for the cross-bonding of a single watersensing wire in each cable, L1, L2, L3. In FIG. 10 the designationscorrespond to the designations used in FIG. 8 and in FIG. 6. Thus, thecross-bonding device CBD has a housing SBDH to which not only the screencross-bonding connection cables SCBCR, SCBCS, SCBCT are inserted, butthrough which also the water sensing wire cross-bonding connectioncables RR, RL; SR, SL; TR, TL are inserted.

The connection plates or connection rails RAR, RAS, RAT additionallycarry a cross-bonding wire RAR′, RAS′, RAT′ which perform the samefunction as the cross-bonding wires in FIG. 9 a. In FIG. 10, the watersensing wire cross-connection cables are preferably coaxial cableshaving a screen and core conductor as shown in FIG. 7. Each coreconductor RR_(C), SL_(C), TR_(C) of the left hand side coaxial cable isconnected to the respective connection line RAR′, RAS′, RAT′ provided inan insulated manner on the connection rails RAR, RAS, RAT. Therespective screen RS_(S), SR_(S), TR_(S) are directly connected with theconnection rails RAR, RAS, RAT, as shown in FIG. 10. The respectivearrestors A_(1R), A_(2R), A_(3R) are preferably connected between arespective core and screen. A similar connection is made on the otherside of the connection line RAS′, RAR′, RAT′ for the left hand sidecoaxial cables. That is, the conductor cores RL_(C), SL_(C), TL_(C) aredirectly connected with the other end of the connection cable RAS′,RAR′, RAT′ and the screen RL_(S), SL_(S), TL_(S) are respectivelyconnected directly to the connection rails RAS, RAT, RAR. A respectivearrestor A_(1L), A_(2L), A_(3L) is again preferably connected betweenthe respective screen and core conductor.

Thus, the cross-bonding device CBD in FIG. 10 directly achieves thecross-bonding for the single water sensing wire and the screens in acircuit connection as described in FIG. 6.

The primary advantage of using only one cross-bonding box CBB is thatthe water sensor wires are invariably cross-bonded in the same manner,electrically and mechanically, and that thus the cable resistances haveapproximately the same complex values such that excess voltages duringfast electrical transient conditions can be avoided.

It should also be noted that the cross-bonding box CBB in FIG. 10 can beconfigured for coaxial cables having two or more core conductors forcross-bonding of two or more water sensing wires or for the selection ofone of them. In this case, the cross-bonding rails RAR, RAS, RAT carry aplurality of connection cables which are respectively connected with thecore-conductors of the respective water sensing wire cross-bondingconnection cable.

Fifth Embodiment

As already described for example with reference to FIG. 7, at eachcross-bonding location CBL it is necessary to lead out the water sensingwires and the screens of the respective cable sections and to connectthem to the respective coaxial cross-bonding connection devices. FIG. 11shows an embodiment of a joint CC1, CC2, CC3 which is schematicallyillustrated in FIG. 7. That is, in FIG. 11 a cross-bonding location isin fact at a location where the conductor cores are joined as indicatedwith the reference numeral 23 in FIG. 11.

In FIG. 11 reference numeral 31 designates an outer layer of theconductor core connection, reference numeral 30 is a left joint,reference numeral 27 is a water proof tape, reference numeral 29 is aprotoden resin, reference numeral 25 describes a water proof tape at thecross-bonding cable lead-out portion and reference numerals 32, 33designate a holding bracket of the cross-bonding connection cablelead-out device LOUTD of the respective joint CC1, CC2, CC3.

As shown in FIG. 11, on the left-hand side, the left-hand side cablecontains a left-hand side water sensing wire 7 ₁ which is connected withthe core RR_(c) of the wire cross-bonding cable RR. The screen RR_(s) ofthe wire cross-bonding cable RR is connected to an insulated copperconductor 24provided on the left side within the cable construction. Ascreen cross-bonding connection cable SCBCR has its core SCBCRcconnected to the insulated copper conductor 24. Likewise, the insulatedcopper conductor 26 from the right hand side cable L1′ is connected tothe screen SCBCR_(S) through a screw connection.

A right-hand side water sensing wire 7 _(R) is led out from the cableL1′ and is connected with the core RL_(c) of the wire cross-bondingconnection cable RL. The screen RL_(s) is connected to the right-handside copper conductor 26. The outer brackets 32, 33, preferably a singlebracket 32, 33 extending like a tube around the cable joint, hasadditional openings for the wire cross-bonding connection cables RR, RLto be led out together with the screen cross-bonding cable SCBCRparallelly. Of course, the joint CC1 shown in FIG. 11 is provided threetimes for allowing the respective connections of the cables of the R, Sand T phase as shown in FIG. 7. Furthermore, it should be noted that ofcourse it is also possible that the wire cross-bonding connection cablesRR, RL in FIG. 11 have more than one core conductor for being connectedwith more than one water sensing wire although FIG. 11 only shows theconnection for a single water sensing wire 7 _(L), 7 _(R) in therespective cable section.

INDUSTRIAL APPLICABILITY

According to the present invention a cable arrangement is provided inwhich the screen and the water sensing wires are on the same potentialas much as possible in steady-state and transient conditions. Since thewater sensing wires as well as the screens are cross-bonded in the samecyclic order potential differences between the screen and the watersensing wires are reduced. Furthermore, cross-bonding devices inaccordance with the invention can be provided which enable to matchimpedances of the water sensing wire connections and the screenconnections. Thus, the invention provides a cable arrangement which canavoid problems due to induction voltages caused by the rated current inthe conductors, caused by short circuits in the conductors or caused bya lightning or other high voltage generating effects. Thus, the presentinvention can preferably be used in any high power transmission systemwhere high power needs to be transmitted over considerable distanceslike over 1-2 km. Furthermore, it should be noted that variousmodifications and variations are possible for a skilled person on thebasis of the above teachings. Therefore, the scope of the presentinvention is not limited to the above descriptions or the contents ofthe claims. What has been described above is only what the inventorspresently conceive as the best mode of the invention and furtherembodiments are possible on the basis of the present specification.

Reference numerals in the claims only serve clarification purposes anddo not limit the scope of these claims.

1. A three-phase high voltage cable arrangement for transmitting powerfrom a first location to a second location including a first, second andthird high voltage cable, each high voltage cable having a conductor anda screen wherein the screens are cross-bonded twice over said distanceat particular cross-bonding locations to cancel out the screen voltages,said first, second and third cable each comprising at least one watersensing wire for sensing water intrusion into the respective cable, saidwater sensing wires being cross-bonded twice over said distance at saidcross-bonding locations wherein the cross-bonding of the water sensingwires is performed in the same cyclic order as the cross-bonding of thescreens to cancel out difference voltages between the water sensor wiresand the cable screens.
 2. A cable arrangement according to claim 1,wherein said cable arrangement comprises a first, second and third cablesection each comprising said first, second and third cable, saidcross-bonding locations being at a respective joint at which therespective cores of the cables are connected.
 3. A cable arrangementaccording to claim 1, wherein said cable arrangement comprises a first,second and third cable section each comprising said first, second andthird cable, said cross-binding locations being located anywhere alongthe length of the cable arrangement where the cable coating is openedfor cross-bonding.
 4. A cable arrangement according to claim 1 or 2,wherein at each cross bonding location a first, second and third pair ofwater sensing wire cross-bonding connection cables are connected withthe respective water sensing wires and a first, second and third screencross-bonding connection cable connected with the respective screens ofthe respective cables are provided for connection with a water sensingwire cross-bonding device and a screen cross-bonding device.
 5. A cablearrangement according to claim 4, wherein said screen cross-bondingdevice and said water sensing wire cross-bonding device are arranged intwo different cross-bonding boxes.
 6. A cable arrangement according toclaim 4, wherein said screen cross-bonding device and said water sensingwire cross-bonding device are arranged in a single common cross-bondingbox.